1. Field of the Invention
This invention relates to equipments used to manufacture integrated circuits and more particularly to wafer disk pads (i.e., wafer clamps) for holding semiconductor wafers in place during wafer fabrication operations.
2. Description of the Relevant Art
Integrated circuits are typically manufactured using a series of semiconductor wafer fabrication operations. Such operations are used to form multiple integrated ciruits upon and within an exposed surface of a semiconductor wafer. As defined herein, the four basic wafer fabrication operations are layering, patterning, doping, and heat treatments. Many wafer fabrication equipments include wafer disk pads for holding semiconductor wafers in place during wafer fabrication operations. Such equipments include ion implantation devices and various types of deposition devices (e.g., sputter deposition devices, chemical vapor deposition devices, etc.).
Ion implantation is one method of forming doped regions (i.e., regions of n-type or p-type dopant atoms) within a surface of a semiconductor wafer. Ion implantation is a physical process in which dopant atoms are ionized, accelerated to a velocity high enough to penetrate the surface of a semiconductor wafer, focused into a narrow beam, and scanned as a beam across the surface of a semiconductor wafer. Dopant ions impacting the surface of the wafer enter the wafer and come to rest below the surface. Offering a high level of control over the location and number of dopant ions placed within the surface of a semiconductor wafer, ion implantation is widely used in the manufacture of integrated circuits with submicron feature sizes.
FIG. 1 is a cross-sectional view of a portion of an exemplary ion implantation device 10. Such an ion implantation device is the model Nova NV-10 manufactured by the Eaton Corp. (Beverly, Mass.). Ion implantation device 10 includes a beam chamber 12 coupled to a process chamber 14. Beam chamber 12 and process chamber 14 are evacuated during ion implantation. Process chamber 14 includes a process chamber base 16 and a process chamber cover 18. Ion implantation is carried out with process chamber cover 18 in a raised position as shown. A wafer disk 20 is mounted on one side of process chamber cover 18, and rotary wafer disk positioner 22 is coupled to process chamber cover 18 on the opposite side. Process chamber cover 18 is hinged to allow the loading and unloading of semiconductor wafers from wafer disk pads attached to wafer disk 20. Such loading and unloading is performed with process cover 18 in a lowered position 24.
Multiple semiconductor wafers are mounted within wafer disk pads attached to the outer periphery of wafer disk 20. During an ion implantation procedure, a process chamber positioner 26 moves process chamber 14 vertically relative to beam chamber 12, and rotary wafer disk positioner 22 rotates wafer disk 20 in order to selectively position the semiconductor wafers within process chamber 14. Process chamber positioner 26 and rotary wafer disk poisitioner 22 work together in order to affect mechanical scanning of a stationary dopant ion beam 28 over surfaces of the semiconductor wafers. An aperture 30 in process chamber base 16 allows gaseous communication between beam chamber 12 and process chamber 14, and also allows dopant ion beam 28 to enter process chamber 14 from beam chamber 12. A sliding seal 32 is used to keep air at atmospheric pressure from entering evacuated process chamber 14 and beam chamber 12.
FIG. 2 is a front elevation view of wafer disk 20 of ion implantation device 10 as seen from beam chamber 12 during an ion implantation procedure. Wafer disk 20 may include ten wafer disk pads 34 arranged about the periphery of wafer disk 20 and configured to hold ten semiconductor wafers 36 in place during an ion implantation procedure. Wafer disk 20 also includes a Faraday slot 38 used to measure wafer dopant dose level.
FIG. 3 is a perspective view of an exemplary wafer disk pad 34. Wafer disk pad 34 includes a clamp member 36 hingably attached to a base plate 38. Wafer disk pad 34 also includes a resilient member (e.g., a spring) which urges clamp member 36 toward base plate 38. Base plate 38 includes a flat, circular pad 40 for receiving a backside surface of a semiconductor wafer. Clamp member 36 includes a clamp base 42, two clamp arms 44a and 44b, two clamp fingers 46a and 46b, and a single clamp handle 48. Clamp base 42 is hingably attached a back portion of an upper surface of base plate 38. Clamp arms 42a and 42b extend along opposite sides of base plate 38 toward a frontside surface of wafer disk pad 34. Clamp fingers 46a and 46b extend perpendicularly from respective clamp arms 44a and 44b, and are directed toward one another and the center of base plate 38. Handle 48 is attached to the end of clamp arm 44a nearest clamp finger 46a such that handle 48 is on the left side of wafer disk pad 34.
Wafer disk pad 34 is shown in an open position in FIG. 3. In the open position, clamp arms 42a-b are raised, and a semiconductor wafer may be loaded into or unloaded from wafer disk pad 34. In a closed position, clamp fingers 46a-b contact an outer perimeter of a semiconductor wafer positioned upon pad 40. The resilient member which urges clamp member 36 toward base plate 38 in the closed position allows wafer disk pad 34 to hold the semiconductor wafer in place.
Base plate 38 includes a rectangular opening 50 to facilitate the loading of a semiconductor wafer into and the unloading of a semiconductor wafer from wafer disk pad 34 using a pair of tweezers. Opening 50 is located in the center of the frontside surface of base plate 38.
Tweezers undesirably contact and exert pressure upon both frontside and backside major surfaces of a semiconductor wafer in order to grip the wafer. The tweezer tip which contacts the frontside surface, upon which active devices are formed, may introduce contaminants which deleteriously affect device operation. In addition, the pressure which must be exerted by the tweezer tips in order to grip the wafer may cause physical damage to the wafer.
For the above reasons vacuum wands have largely replaced tweezers as preferred semiconductor wafer transport tools. A typical vacuum wand has a tip, stem, and handle. The stem is a vacuum tube which connects the tip to the handle. The tip has a flat upper surface having an orifice located substantially in the center. During use, the tip is brought into contact with the underside surface of a semiconductor wafer. Pressing a button on the handle causes air to be drawn into the orifice, creating a vacuum between the tip and the wafer which couples the wafer to the tip. Releasing the button breaks the vacuum and allows the wafer to separate from the tip. As the vacuum wand does not contact the frontside surface of the wafer, the vacuum wand cannot introduce contaminants onto the frontside surface. In addition, the vacuum force which holds the wafer to the tip is not great enough to cause physical damage to the wafer.
Several problems arise when trying to use a vacuum wand with wafer disk pad 34 of FIG. 3. First, the tips of most commercially available vacuum wands are too large to fit into opening 50 designed for tweezers. Second, located in the center of one side of wafer disk pad 34, opening 50 is not convenient for use by either right-handed or left-handed operators facing wafer disk pad 34. A right-handed operator must position his or her body on the left side of opening 50 and angle his or her body in relation to wafer disk pad 40 in order to comfortably insert a wafer into or remove a wafer from wafer disk pad 34. A left-handed operator must position his or her body on the right side of opening 50 and again angle his or her body in relation to wafer disk pad 40 in order to comfortably insert a wafer into or remove a wafer from wafer disk pad 34. Third, single handle 48 is only convenient for right-handed operators. Left-handed operators hold vacuum wands in their left hands and must reach across with their right hands to operate handle 48.
Experience with wafer disk pad 34 of FIG. 3 in a manufacturing environment has shown that due to the above shortcomings operators will often not use opening 50 for vacuum wand wafer loading and unloading. Instead, they will force the tip of the vacuum wand between the wafer and base plate 38 to the right or the left of opening 50. As a result, pad 40 is damaged during wafer loading and unloading, and must be replaced frequently. In addition, loose pieces of pad 40 become particulate contaminants within process chamber 14 during ion implantation operations.
It would thus be beneficial to have a wafer disk pad having one or more wafer loading points at convenient locations to facilitate vacuum wand wafer loading and unloading. Such a wafer disk pad would significantly reduce damage to pad 40 and the resultant particulate contaminant problem within process chamber 14.